Refactor code to separate Model from Controller

* Note handling functions moved to a new class in a separate file.
* secure_remove tweaked to remove all existing files in one call.
More separation changes

* Moved file checks from controller to the model
* Simplified HMAC digest comparison
* Simplified data dir specification to make for easier moves.
Moved utility functions to utils.py
	modified:   note.py

HMAC comparison should be done before we attempt to uncompress, otherwise we
have a timing attack.

Additionally HMAC comparison should be done in constant time, again to prevent
timing attacks.

See http://codahale.com/a-lesson-in-timing-attacks/ for example.
Stupid typo
Merge pull request #31 from atoponce/refactor

Refactor code to separate Model from Controller. note.py created for handling the note work, and utils.py for external utility functions for various operations.